1. Field of the Invention
The present invention relates to a special reproduction function of an apparatus for reproducing information recorded on a disk (such as an optical disk reproducing apparatus), and more particularly to a control unit suitable to rapidly move an actuator of a reader from one track to another on which information has been recorded.
2. Description of the Prior Art
In a known optical disk reproducing apparatus, when pickup means for reading information recorded on the disk is to be moved from a current track to a track displaced therefrom by several tens to several hundreds tracks, it is usually moved to an adjacent track by one track by incremental movement or jump, and this operation is repeated by a desired number of times. In the jump operation, a tracking control loop which has a function to cause the pickup means to precisely follow the target track is opened, and a certain power product is applied to the pickup means until it reaches a midpoint between the adjacent tracks. After the pickup means has passed the midpoint, the tracking control loop is closed and a power product which is opposite in polarity and equal in magnitude to the previously applied power product is applied to move the pickup means to the adjacent track. (For example, Japanese Unexamined patent publication No. 58-187086).
A loss of energy during each jump operation can be automatically corrected by the tracking control loop but a time is requried to complete the correction. As a result, a certain margin time is required from the end of the first jump operation to the start of the next jump operation. In this system, therefore, an average pickup velocity is much lower than the highest possible velocity of the pickup means. Instead of the method in which the pickup means is moved to the adjacent track by one track in every jump operation, the pickup means may be moved by a plurality of tracks in every jump operation.
In such multi-jump operation, feed operation for the pickup on which an actuator is mounted is temporarily stopped and only the actuator is moved. The actuator is usually supported to the pickup by a suspension spring. Thus, after the actuator has been moved to the target track, the pickup is moved to follow it. This is essentially different from a random access function in which the pickup is rapidly moved and then the one-track jump of the actuator is repeated around the target track to move the actuator onto the target track.
The multi-jump operation is used when it is required to precisely and rapidly move the actuator by a predetermined number of tracks within a movable range of the actuator permitted on the pickup. However, when the actuator is continuously moved over a plurality of tracks, an affect of a resonance characteristic of the actuator of the pickup means remarkably appears and the actuator may be vibrated during the movement across the tracks. As a result, an instantaneous velocity always varies and the setting of the actuator on the target track and the jumping of the actuator by the predetermined number of tracks are difficult to attain.